"The next day, the previous day"
Translation:Następny dzień, poprzedni dzień
It makes little sense to construct a a framework of rules and exceptions for this, because there would be just too much to memorise.
For example, you could make a rule for -edni, but then you'd have to memorise bezwiedny, biedny, wredny, wybredny, mimowiedny, which are exceptions.
We don't actually say "przyszły dzień". After Alik did some digging, I think it's safe to say that "przyszły", when it regards a single day, must be at least a week from now. For example an article printed on Friday, 9th of September and saying "przyszła sobota" for "next Saturday" actually meant Saturday 17th of September, not the closest one on the 10th.